docs: def com_google_fonts_check_family_control_chars(ttFonts):
    """Does font file include unacceptable control character glyphs?"""
    # list of unacceptable control character glyph names
    # definition includes the entire control character Unicode block except:
    #    - .null (U+0000)
    #    - CR (U+000D)
    unacceptable_cc_list = [
        "uni0001",
        "uni0002",
        "uni0003",
        "uni0004",
        "uni0005",
        "uni0006",
        "uni0007",
        "uni0008",
        "uni0009",
        "uni000A",
        "uni000B",
        "uni000C",
        "uni000E",
        "uni000F",
        "uni0010",
        "uni0011",
        "uni0012",
        "uni0013",
        "uni0014",
        "uni0015",
        "uni0016",
        "uni0017",
        "uni0018",
        "uni0019",
        "uni001A",
        "uni001B",
        "uni001C",
        "uni001D",
        "uni001E",
        "uni001F"
    ]
  
    # a dict with key:value of font path that failed check : list of unacceptable glyph names
    failed_font_dict = {}
  
    for ttFont in ttFonts:
      font_failed = False
      unacceptable_glyphs_in_set = []  # a list of unacceptable glyph names identified
      glyph_name_set = set(ttFont["glyf"].glyphs.keys())
      fontname = ttFont.reader.file.name
  
      for unacceptable_glyph_name in unacceptable_cc_list:
        if unacceptable_glyph_name in glyph_name_set:
          font_failed = True
          unacceptable_glyphs_in_set.append(unacceptable_glyph_name)
  
      if font_failed:
          failed_font_dict[fontname] = unacceptable_glyphs_in_set
  
    if len(failed_font_dict) > 0:
      unacceptable_cc_report_string = "The following unacceptable control characters were identified:\n"
      for fnt in failed_font_dict.keys():
        unacceptable_cc_report_string += " {}: {}\n".format(
            fnt, ", ".join(failed_font_dict[fnt])
        )
      yield FAIL, ("{}".format(unacceptable_cc_report_string))
    else:
      yield PASS, ("Unacceptable control characters were not identified.")